The effectiveness of two methods of presurgical hand preparation - 10 min. routine scrub and 90 sec. Hydroscrub - in reduction of microbial numbers under fingernails was determined. The finding of high postscrub microbial counts under fingernails is of particular interest and significance in view of the results relating to the relatively low counts on fingertips. The extremely high number of microorganisms remaining in the subungual areas should alert every member of the surgical team to the possible danger of until now unrecognized failure of proper hand degerming prior to surgery. On the basis of the results of this study, it is concluded that 1 Degerming of the areas under the fingernails by present methods is not satisfactory 2 Evaluation of the efficacy of various antiseptic agents and scrub techniques should include determination of the microbial counts in the subungual areas in addition to the assays of microbial population on the skin of hands and 3 The possible implication of the subungual microorganisms in the development of postsurgical infection should be investigated and 4 A modification of the methods currently used or, possible, a new approach to the effective reduction of microbial population under the fingernails is necessary.